Determination of the oxidation states of manganese in brain, liver, and heart mitochondria

Examining the Oxidation States of Metals in Aerosols Emitted by Electronic Cigarettes

Electronic cigarettes (ECs) emit many toxic substances, including metals, that can pose a threat to users and the environment. The toxicity of the emitted metals depends on their oxidation states. Hence, this study examines the oxidation states of metals observed in EC aerosols. X-ray photoelectron spectroscopy analysis of the filters that collected EC aerosols identified the oxidation states of five primary metals (based on surface sample analysis), including chromium(III) (close to 100%) under low power setting while a noticeable amount of chromium(VI) (15%) at higher power settings of the EC, and copper(II) (100%), zinc(II) (100%), nickel(II) (100%), lead(II) (65%), and lead(IV) (35%) regardless of power settings. This observation indicates that the increased temperature due to higher power settings could alter the oxidation states of certain metals. We noted that many metals were in their lesser toxic states; however, inhaling these metals may still pose health risks.

Small-Molecule Fluorescent Probes for Binding- and Activity-Based Sensing of Redox-Active Biological Metals

Although transition metals constitute less than 0.1% of the total mass within a human body, they have a substantial impact on fundamental biological processes across all kingdoms of life. Indeed, these nutrients play crucial roles in the physiological functions of enzymes, with the redox properties of many of these metals being essential to their activity. At the same time, imbalances in transition metal pools can be detrimental to health. Modern analytical techniques are helping to illuminate the workings of metal homeostasis at a molecular and atomic level, their spatial localization in real time, and the implications of metal dysregulation in disease pathogenesis. Fluorescence microscopy has proven to be one of the most promising non-invasive methods for studying metal pools in biological samples. The accuracy and sensitivity of bioimaging experiments are predominantly determined by the fluorescent metal-responsive sensor, highlighting the importance of rational probe design for such measurements. This review covers activity- and binding-based fluorescent metal sensors that have been applied to cellular studies. We focus on the essential redox-active metals: iron, copper, manganese, cobalt, chromium, and nickel. We aim to encourage further targeted efforts in developing innovative approaches to understanding the biological chemistry of redox-active metals.

Trypanosoma brucei Mitochondrial DNA Polymerase POLIB Contains a Novel Polymerase Domain Insertion That Confers Dominant Exonuclease Activity

Trypanosoma brucei and related parasites contain an unusual catenated mitochondrial genome known as kinetoplast DNA (kDNA) composed of maxicircles and minicircles. The kDNA structure and replication mechanism are divergent and essential for parasite survival. POLIB is one of three Family A DNA polymerases independently essential to maintain the kDNA network. However, the division of labor among the paralogs, particularly which might be a replicative, proofreading enzyme, remains enigmatic. De novo modeling of POLIB suggested a structure that is divergent from all other Family A polymerases, in which the thumb subdomain contains a 369 amino acid insertion with homology to DEDDh DnaQ family 3'-5' exonucleases. Here we demonstrate recombinant POLIB 3'-5' exonuclease prefers DNA vs RNA substrates and degrades single- and double-stranded DNA nonprocessively. Exonuclease activity prevails over polymerase activity on DNA substrates at pH 8.0, while DNA primer extension is favored at pH 6.0. Mutations that ablate POLIB polymerase activity slow the exonuclease rate suggesting crosstalk between the domains. We show that POLIB extends an RNA primer more efficiently than a DNA primer in the presence of dNTPs but does not incorporate rNTPs efficiently using either primer. Immunoprecipitation of Pol I-like paralogs from T. brucei corroborates the pH selectivity and RNA primer preferences of POLIB and revealed that the other paralogs efficiently extend a DNA primer. The enzymatic properties of POLIB suggest this paralog is not a replicative kDNA polymerase, and the noncanonical polymerase domain provides another example of exquisite diversity among DNA polymerases for specialized function.

Human Mitochondrial DNA Polymerase Metal Dependent UV Lesion Bypassing Ability

Human mitochondrial DNA contains more UV-induced lesions than the nuclear DNA due to lack of mechanism to remove bulky photoproducts. Human DNA polymerase gamma (Pol γ) is the sole DNA replicase in mitochondria, which contains a polymerase (pol) and an exonuclease (exo) active site. Previous studies showed that Pol γ only displays UV lesion bypassing when its exonuclease activity is obliterated. To investigate the reaction environment on Pol γ translesion activity, we tested Pol γ DNA activity in the presence of different metal ions. While Pol γ is unable to replicate through UV lesions on DNA templates in the presence of Mg²⁺, it exhibits robust translesion DNA synthesis (TLS) on cyclobutane pyrimidine dimer (CPD)-containing template when Mg²⁺ was mixed with or completely replaced by Mn²⁺. Under these conditions, the efficiency of Pol γ′s TLS opposite CPD is near to that on a non-damaged template and is 800-fold higher than that of exonuclease-deficient Pol γ. Interestingly, Pol γ exhibits higher exonuclease activity in the presence of Mn²⁺ than with Mg²⁺, suggesting Mn²⁺-stimulated Pol γ TLS is not via suppressing its exonuclease activity. We suggest that Mn²⁺ ion expands Pol γ′s pol active site relative to Mg²⁺ so that a UV lesion can be accommodated and blocks the communication between pol and exo active sites to execute translesion DNA synthesis.

Metal ion fluxes controlling amphibian fertilization

Mammalian oocytes undergo major changes in zinc content and localization to be fertilized, the most striking being the rapid exocytosis of over 10 billion zinc ions in what are known as zinc sparks. Here, we report that fertilization of amphibian Xenopus laevis eggs also initiates a zinc spark that progresses across the cell surface in coordination with dynamic calcium waves. This zinc exocytosis is accompanied by a newly recognized loss of intracellular manganese. Synchrotron-based X-ray fluorescence and analytical electron microscopy reveal that zinc and manganese are sequestered in a system of cortical granules that are abundant at the animal pole. Through electron-nuclear double-resonance studies, we rule out Mn²⁺ complexation with phosphate or nitrogenous ligands in intact eggs, but the data are consistent with a carboxylate coordination environment. Our observations suggest that zinc and manganese fluxes are a conserved feature of fertilization in vertebrates and that they function as part of a physiological block to polyspermy.

Maintaining Translational Relevance in Animal Models of Manganese Neurotoxicity

Manganese is an essential metal, but elevated brain Mn concentrations produce a parkinsonian-like movement disorder in adults and fine motor, attentional, cognitive, and intellectual deficits in children. Human Mn neurotoxicity occurs owing to elevated exposure from occupational or environmental sources, defective excretion (e.g., due to cirrhosis), or loss-of-function mutations in the Mn transporters solute carrier family 30 member 10 or solute carrier family 39 member 14. Animal models are essential to study Mn neurotoxicity, but in order to be translationally relevant, such models should utilize environmentally relevant Mn exposure regimens that reproduce changes in brain Mn concentrations and neurological function evident in human patients. Here, we provide guidelines for Mn exposure in mice, rats, nematodes, and zebrafish so that brain Mn concentrations and neurobehavioral sequelae remain directly relatable to the human phenotype.

The effects of manganese overexposure on brain health

Manganese (Mn) is the twelfth most abundant element on the earth and an essential metal to human health. Mn is present at low concentrations in a variety of dietary sources, which provides adequate Mn content to sustain support various physiological processes in the human body. However, with the rise of Mn utility in a variety of industries, there is an increased risk of overexposure to this transition metal, which can have neurotoxic consequences. This risk includes occupational exposure of Mn to workers as well as overall increased Mn pollution affecting the general public. Here, we review exposure due to air pollution and inhalation in industrial settings; we also delve into the toxic effects of manganese on the brain such as oxidative stress, inflammatory response and transporter dysregulation. Additionally, we summarize current understandings underlying the mechanisms of Mn toxicity.

Nudt8 is a novel CoA diphosphohydrolase that resides in the mitochondria

CoA regulates energy metabolism and exists in separate pools in the cytosol, peroxisomes, and mitochondria. At the whole tissue level, the concentration of CoA changes with the nutritional state by balancing synthesis and degradation; however, it is currently unclear how individual subcellular CoA pools are regulated. Liver and kidney peroxisomes contain Nudt7 and Nudt19, respectively, enzymes that catalyze CoA degradation. We report that Nudt8 is a novel CoA-degrading enzyme that resides in the mitochondria. Nudt8 has a distinctive preference for manganese ions and exhibits a broader tissue distribution than Nudt7 and Nudt19. The existence of CoA-degrading enzymes in both peroxisomes and mitochondria suggests that degradation may be a key regulatory mechanism for modulating the intracellular CoA pools.

Emerging chemical tools and techniques for tracking biological manganese

This frontier article discusses chemical tools and techniques for tracking and imaging Mn ions in biology.

Could male reproductive system be the main target of subchronic exposure to manganese in adult animals?

Manganese (Mn) is one of the most common chemical elements on Earth and an essential micronutrient in animal organism. However, in supraphysiological levels and long-term exposures, it is a potential toxicant. Although nervous system is the most studied in relation to Mn toxicity, other tissues can have their function impaired by Mn in high doses. The present study investigated the possible adverse effects of subchronic exposure to supraphysiologic level of Mn (5 mg/kg or 15 mg/kg, intraperitoneally) on reproductive, neurobehavioral, renal and hepatic parameters of male rats. For the first time, the vulnerability of these parameters to Mn was concomitantly investigated. While our results demonstrate that Mn treatments were not sufficient to produce a marked effect of neurotoxic, hepatotoxic or renal toxicity in adult rats, we found typical indicators of reproductive toxicity such as histopathological changes (major in testes and epididymis) and impaired sperm concentration and quality. Mn, under these experimental conditions, seems to exert reproductive toxicity by different testicular mechanisms, i.e. direct and indirect action on germ cells. On the other hand, exposure to Mn did not change the pattern of cognitive and emotional behaviors and the histological organization of kidneys of experimental rats. The liver showed a weight increasement and hidropic degeneration, probable due to the detoxification overload. In summary, for the first time it was demonstrated that adult male reproductive system was more sensitive to Mn toxicity than nervous, hepatic and renal systems, although nervous system is known as the main target tissue of this metal.

Ultrastructural Changes of Caudate Nucleus in Mice Chronically Treated with Manganese

Manganese (Mn) is able to cross the blood-brain barrier and induces functional and structural alterations during the intoxication by this metal. Therefore, the effects of chronic administration of Mn in the caudate nucleus of mice were evaluated by electron microscopy. Male albino mice were injected intraperitoneally with MnCl2 (5 mg/kg/d) 5 d per week during 9 weeks. The control group received only 0.9% of NaCl solution. The caudate nuclei were extracted and subsequently processed to be observed on a conventional transmission electron microscope at 2, 4, 6, and 9 weeks after treatment. A high percentage of vacuolated and swollen mitochondria were found throughout all the analyzed periods. Myelin disarrangement and ultrastructural alterations related to edema were observed increased in Mn-treated mice at week 9. Granular degeneration of myelin at week 9 accompanied with deposition of electron dense granules in the neuropil was also observed. Edema in neuropil and glial cells was detected from week 2 to week 9 accompanied by swollen mitochondria. Neuronal bodies, synaptic terminals, and perivascular cells were found swollen. Decreased electron density in postsynaptic areas and decreased and dispersed synaptic vesicles in presynaptic areas were noted in Mn-treated animals. Some neurons from Mn-treated mice showed cisternae dilation of the Golgi apparatus. These results suggest that Mn-treatment produces structural alterations in the caudate nucleus that could be responsible for some of the neurotoxic effects of this metal.

Determination of Trace Metals and Essential Minerals in Selected Fruit Juices in Minna, Nigeria

Levels of trace metals and essential minerals in selected fruit juice samples purchased from Minna were determined using atomic absorption spectrophotometer (AAS) and Flame photometer. From the obtained result, Cu, Fe, Mn, Na, and Zn were present in all the samples, while Cd, Pb, and Cr were not detectable in all the samples. Concentrations of K range between 1.31 ± 0.10 and 41.20 ± 0.10 mg/100 mL, Na between 15.47 ± 0.15 and 3.50 ± 0.20 mg/100 mL, Mn between Nd and 0.27 ± 0.08 mg/100 mL, Fe between Nd and 0.90 ± 0.05 mg/100 mL, Cu between Nd-0.60 ± 0.00 mg/100 mL, and Zn between Nd-0.09 ± 0.01 mg/100 mL, respectively. The trace metal levels in all the samples were within permissible limit as recommended by WHO for edible foods and drinks and could therefore be taken to compliment the deficiency of these essential minerals from other food sources.

Manganese-induced effects on cerebral trace element and nitric oxide of Hyline cocks

Exposure to Manganese (Mn) is a common phenomenon due to its environmental pervasiveness. To investigate the Mn-induced toxicity on cerebral trace element levels and crucial nitric oxide parameters on brain of birds, 50-day-old male Hyline cocks were fed either a commercial diet or a Mn-supplemented diet containing 600, 900, 1,800 mg kg(-1). After being treated with Mn for 30, 60, and 90 days, the following were determined: the changes in contents of copper (Cu), iron (Fe), zinc (Zn), calcium (Ca), selenium (Se) in brain; inducible nitric oxide synthase-nitric oxide (iNOS-NO) system activity in brain; and histopathology and ultrastructure changes of cerebral cortex. The results showed that Mn was accumulated in brain and the content of Cu and Fe increased. However, the levels of Zn and Se decreased and the Ca content presented no obvious regularity. Exposure to Mn significantly elevated the content of NO and the expression of iNOS mRNA. Activity of total NO synthase (T NOS) and iNOS appeared with an increased tendency. These findings suggested that Mn exposure resulted in the imbalance of cerebral trace elements and influenced iNOS in the molecular level, which are possible underlying nervous system injury mechanisms induced by Mn exposure.

Novel bioimaging techniques of metals by laser ablation inductively coupled plasma mass spectrometry for diagnosis of fibrotic and cirrhotic liver disorders

Background and Aims

Hereditary disorders associated with metal overload or unwanted toxic accumulation of heavy metals can lead to morbidity and mortality. Patients with hereditary hemochromatosis or Wilson disease for example may develop severe hepatic pathology including fibrosis, cirrhosis or hepatocellular carcinoma. While relevant disease genes are identified and genetic testing is applicable, liver biopsy in combination with metal detecting techniques such as energy-dispersive X-ray spectroscopy (EDX) is still applied for accurate diagnosis of metals. Vice versa, several metals are needed in trace amounts for carrying out vital functions and their deficiency due to rapid growth, pregnancy, excessive blood loss, and insufficient nutritional or digestive uptake results in organic and systemic shortcomings. Established in situ techniques, such as EDX-ray spectroscopy, are not sensitive enough to analyze trace metal distribution and the quantification of metal images is difficult.

Methods

In this study, we developed a quantitative biometal imaging technique of human liver tissue by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in order to compare the distribution of selected metals in cryo-sections of healthy and fibrotic/cirrhotic livers.

Results

Most of the metals are homogeneous distributed within the normal tissue, while they are redirected within fibrotic livers resulting in significant metal deposits. Moreover, total iron and copper concentrations in diseased liver were found about 3-5 times higher than in normal liver samples.

Conclusions

Biometal imaging via LA-ICP-MS is a sensitive innovative diagnostic tool that will impact clinical practice in identification and evaluation of hepatic metal disorders and to detect subtle metal variations during ongoing hepatic fibrogenesis.

Manganese-induced effects on testicular trace element levels and crucial hormonal parameters of Hyline cocks

Manganese (Mn) is an essential element required for normal development and reproduction. However, little is known about the reproductive toxicity of Mn in birds. To investigate the Mn-induced toxicity on testicular trace element levels and crucial hormonal parameters on male reproduction in birds, 50-day-old male Hyline cocks were fed either a commercial diet or a Mn-supplemented diet. The changes in contents of copper (Cu), iron (Fe), zinc (Zn), and calcium (Ca) in testis were detected. Hormonal parameters were evaluated including the levels of testosterone (T), luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) in the serum. The mRNA levels of luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) were determined in this study. The results showed that Mn was accumulated in testis, and the content of Cu, Fe, Zn, and Ca decreased. Exposure to Mn significantly lowered the content of T, LH, FSH, and the mRNA expression levels of LHR and FSHR. Levels of T3 and T4 appeared with a decreased tendency, and TSH presented no obvious regularity. It indicated that Mn exposure resulted in the disbalance of testicular trace elements and influenced hormone levels in the molecular level, which may be possible underlying reproductive toxicity mechanism induced by Mn.

Manganese transport via the transferrin mechanism

Excessive manganese (Mn) uptake by brain cells, particularly in regions like the basal ganglia, can lead to toxicity. Mn(2+) is transported into cells via a number of mechanisms, while Mn(3+) is believed to be transported similarly to iron (Fe) via the transferrin (Tf) mechanism. Cellular Mn uptake is therefore determined by the activity of the mechanisms transporting Mn into each type of cell and by the amounts of Mn(2+), Mn(3+) and their complexes to which these cells are exposed; this complicates understanding the contributions of each transporter to Mn toxicity. While uptake of Fe(3+) via the Tf mechanism is well understood, uptake of Mn(3+) via this mechanism has not been systematically studied. The stability of the Mn(3+)Tf complex allowed us to form and purify this complex and label it with a fluorescent (Alexa green) tag. Using purified and labeled Mn(3+)Tf and biophysical tools, we have developed a novel approach to study Mn(3+)Tf transport independently of other Mn transport mechanisms. This approach was used to compare the uptake of Mn(3+)Tf into neuronal cell lines with published descriptions of Fe(3+) uptake via the Tf mechanism, and to obtain quantitative information on Mn uptake via the Tf mechanism. Results confirm that in these cell lines significant Mn(3+) is transported by the Tf mechanism similarly to Fe(3+)Tf transport; although Mn(3+)Tf transport is markedly slower than other Mn transport mechanisms. This novel approach may prove useful for studying Mn toxicity in other systems and cell types.

Genetic risk for Parkinson's disease correlates with alterations in neuronal manganese sensitivity between two human subjects

Manganese (Mn) is an environmental risk factor for Parkinson's disease (PD). Recessive inheritance of PARK2 mutations is strongly associated with early onset PD (EOPD). It is widely assumed that the influence of PD environmental risk factors may be enhanced by the presence of PD genetic risk factors in the genetic background of individuals. However, such interactions may be difficult to predict owing to the complexities of genetic and environmental interactions. Here we examine the potential of human induced pluripotent stem (iPS) cell-derived early neural progenitor cells (NPCs) to model differences in Mn neurotoxicity between a control subject (CA) with no known PD genetic risk factors and a subject (SM) with biallelic loss-of-function mutations in PARK2 and family history of PD but no evidence of PD by neurological exam. Human iPS cells were generated from primary dermal fibroblasts of both subjects. We assessed several outcome measures associated with Mn toxicity and PD. No difference in sensitivity to Mn cytotoxicity or mitochondrial fragmentation was observed between SM and CA NPCs. However, we found that Mn exposure was associated with significantly higher reactive oxygen species (ROS) generation in SM compared to CA NPCs despite significantly less intracellular Mn accumulation. Thus, this report offers the first example of human subject-specific differences in PD-relevant environmental health related phenotypes that are consistent with pathogenic interactions between known genetic and environmental risk factors for PD.

Effects of dietary manganese on Cu, Fe, Zn, Ca, Se, IL-1β, and IL-2 changes of immune organs in cocks

Manganese (Mn) is an essential trace element required for normal development and bodily function. However, little is known about the effect of excessive amounts of Mn in immune organs of poultry. The aim of this study was to investigate the effect of dietary Mn on the content of trace elements, such as copper (Cu), iron (Fe), zinc (Zn), calcium (Ca), and selenium (Se), and the mRNA level of IL-1β and IL-2 in immune organs (spleen, thymus, and bursa of Fabricius) and the content of IL-1β and IL-2 in serum of poultry. Fifty-day-old male Hyline cocks were fed either a commercial diet or a Mn-supplemented diet containing 600, 900, and 1,800 mg/kg. The immune organs were collected at 30, 60, and 90 days, respectively, and the content of trace elements and the mRNA level of IL-1β and IL-2 were examined; the serum were collected and the IL-1β and IL-2 contents detected. The results showed that Mn content in immune organs increased and Fe, Zn, and Ca contents decreased; however, Cu and Se contents showed no difference. IL-1β and IL-2 mRNA levels and IL-1β and IL-2 contents decreased. The present study demonstrates that excess exposure to Mn results in metal accumulations in immune organs. Manganism can disturb the balance of trace elements in immune organs and induce immune suppression in the molecular level; therefore, the immune function of cocks are also suppressed after manganism.

Physical and functional interaction of NCX1 and EAAC1 transporters leading to glutamate-enhanced ATP production in brain mitochondria

Glutamate is emerging as a major factor stimulating energy production in CNS. Brain mitochondria can utilize this neurotransmitter as respiratory substrate and specific transporters are required to mediate the glutamate entry into the mitochondrial matrix. Glutamate transporters of the Excitatory Amino Acid Transporters (EAATs) family have been previously well characterized on the cell surface of neuronal and glial cells, representing the primary players for glutamate uptake in mammalian brain. Here, by using western blot, confocal microscopy and immunoelectron microscopy, we report for the first time that the Excitatory Amino Acid Carrier 1 (EAAC1), an EAATs member, is expressed in neuronal and glial mitochondria where it participates in glutamate-stimulated ATP production, evaluated by a luciferase-luciferin system. Mitochondrial metabolic response is counteracted when different EAATs pharmacological blockers or selective EAAC1 antisense oligonucleotides were used. Since EAATs are Na⁺-dependent proteins, this raised the possibility that other transporters regulating ion gradients across mitochondrial membrane were required for glutamate response. We describe colocalization, mutual activity dependency, physical interaction between EAAC1 and the sodium/calcium exchanger 1 (NCX1) both in neuronal and glial mitochondria, and that NCX1 is an essential modulator of this glutamate transporter. Only NCX1 activity is crucial for such glutamate-stimulated ATP synthesis, as demonstrated by pharmacological blockade and selective knock-down with antisense oligonucleotides. The EAAC1/NCX1-dependent mitochondrial response to glutamate may be a general and alternative mechanism whereby this neurotransmitter sustains ATP production, since we have documented such metabolic response also in mitochondria isolated from heart. The data reported here disclose a new physiological role for mitochondrial NCX1 as the key player in glutamate-induced energy production.

15-Deoxy-Δ12,14-prostaglandin J₂ modulates manganese-induced activation of the NF-κB, Nrf2, and PI3K pathways in astrocytes

Excessive exposure to manganese (Mn) increases levels of oxidative stressors and proinflammatory mediators, such as cyclooxygenase-2 and prostaglandin E(2). Mn also activates nuclear factor-κB (NF-κB), an important mediator of inflammation. The signaling molecule 15-deoxy-Δ12,14-prostaglandin J(2) (15 d-PGJ(2)) is an anti-inflammatory prostaglandin. Here, we tested the hypothesis that 15 d-PGJ(2) modulates Mn-induced activation of astrocytic intracellular signaling, including NF-κB and nuclear factor erythroid 2-related factor (Nrf2), a master regulator of antioxidant transcriptional responses. The results establish that 15 d-PGJ(2) suppresses Mn-induced NF-κB activation by interacting with several signaling pathways. The PI3K/Akt pathway, which is upstream of NF-κB, plays a role in this activation, because (i) pretreatment with 15 d-PGJ(2) (10 μM for 1h) significantly (p<0.01) inhibited Mn (500 μM)-induced PI3K/Akt activation and (ii) inhibition of the PI3K/Akt pathway with LY29004 significantly (p<0.05) decreased NF-κB activation. 15 d-PGJ(2) also significantly (p<0.05) attenuated Mn-induced astrocytic NF-κB activation by inhibiting the Mn-induced phosphorylation of IκB kinase and subsequent IκB-α degradation. Because Mn-induced oxidative stress is also associated with Nrf2 activation, additional studies addressed the ability of 15 d-PGJ(2) to modulate the Nrf2 pathway. 15 d-PGJ(2) significantly (p<0.01) increased Nrf2 expression in whole-cell lysates. Consistent with its pro-oxidant properties, Mn also increased Nrf2 expression. Nevertheless, cotreatment of whole-cell lysates with both Mn and 15 d-PGJ(2) partially suppressed (p<0.01) the 15 d-PGJ(2)-induced increase in astrocytic Nrf2 protein expression. Mn treatment also decreased (p<0.001) expression of DJ-1, a Parkinson disease-associated protein and a stabilizer of Nrf2, and 15 d-PGJ(2) attenuated Mn-induced astrocytic inhibition of DJ-1 expression. Collectively, these results demonstrate that 15d-PGJ(2) exerts a protective effect in astrocytes against Mn-induced inflammation and oxidative stress by modulating the activation of the NF-κB and Nrf2 signaling pathways.

Cellular transport and homeostasis of essential and nonessential metals

Metals can have a number of detrimental or beneficial effects in the cell, but first they must get in. Organisms have evolved transport mechanisms to get metals that are required, or essential into the cell. Nonessential metals often enter the cell through use of the machinery provided for essential metals. Much work has been done to advance our understanding of how these metals are transported across plasma and organelle membranes. This review provides an overview of essential and nonessential metal transport and homeostatic processes.

Calpain activation is involved in acute manganese neurotoxicity in the rat striatum in vivo

Manganese is essential for life, yet chronic exposure to this metal can cause a neurodegenerative disease named manganism that affects motor function. In the present study we have evaluated Mn neurotoxicity after its administration in the rat striatum. The participation of the calcium-dependent protease calpain and the apoptosis-related protease caspase-3, in Mn-induced cell death was monitored in the striatum and globus pallidus. Mn induced the activation of both proteases, although calpain activation seems to be an earlier event. Moreover, while the broad-spectrum caspase inhibitor QVD did not significantly prevent Mn-induced cell death, the specific calpain inhibitor MDL-28170 did. The role of NMDA glutamate receptors on calpain activity was also investigated; blockage of these receptors by MK-801 and memantine did not prevent calpain activation, nor Mn-induced cell death. Finally, studies in striatal homogenates suggest a direct activation of calpain by Mn ions. Altogether the present study suggests that additional mechanisms to excitotoxicity are involved in Mn-induced cell death, placing calpain as an important mediator of acute Mn neurotoxicity in vivo.

Manganese accumulation in the CNS and associated pathologies

Manganese (Mn) is an essential metal for life. It is a key constituent of clue enzymes in the central nervous system, contributing to antioxidant defenses, energetic metabolism, ammonia detoxification, among other important functions. Until now, Mn transport mechanisms are partially understood; however, it is known that it shares some mechanisms of transport with iron. CNS is susceptible to Mn toxicity because it possesses mechanisms that allow Mn entry and favor its accumulation. Cases of occupational Mn exposure have been extensively reported in the literature; however, there are other ways of exposure, such as long-term parental nutrition and liver failure. Manganism and hepatic encephalopathy are the most common pathologies associated with the effects of Mn exposure. Both pathologies are associated with motor and psychiatric disturbances, related in turn to mechanisms of damage such as oxidative stress and neurotransmitters alterations, the dopaminergic system being one of the most affected. Although manganism and Parkinson's disease share some characteristics, they differ in many aspects that are discussed here. The mechanisms for Mn transport and its participation in manganism and hepatic encephalopathy are also considered in this review. It is necessary to find an effective therapeutic strategy to decrease Mn levels in exposed individuals and to treat Mn long term effects. In the case of patients with chronic liver failure it would be worthwhile to test a low-Mn diet in order to ameliorate symptoms of hepatic encephalopathy possibly related to Mn accumulation.

Manganese-enhanced magnetic resonance imaging

Manganese-enhanced magnetic resonance imaging (MEMRI) relies on contrasts that are due to the shortening of the T (1) relaxation time of tissue water protons that become exposed to paramagnetic manganese ions. In experimental animals, the technique combines the high spatial resolution achievable by MRI with the biological information gathered by tissue-specific or functionally induced accumulations of manganese. After in vivo administration, manganese ions may enter cells via voltage-gated calcium channels. In the nervous system, manganese ions are actively transported along the axon. Based on these properties, MEMRI is increasingly used to delineate neuroanatomical structures, assess differences in functional brain activity, and unravel neuronal connectivities in both healthy animals and models of neurological disorders. Because of the cellular toxicity of manganese, a major challenge for a successful MEMRI study is to achieve the lowest possible dose for a particular biological question. Moreover, the interpretation of MEMRI findings requires a profound knowledge of the behavior of manganese in complex organ systems under physiological and pathological conditions. Starting with an overview of manganese pharmacokinetics and mechanisms of toxicity, this chapter covers experimental methods and protocols for applications in neuroscience.

An analysis of the effects of Mn2+ on oxidative phosphorylation in liver, brain, and heart mitochondria using state 3 oxidation rate assays

Manganese (Mn) toxicity is partially mediated by reduced ATP production. We have used oxidation rate assays--a measure of ATP production--under rapid phosphorylation conditions to explore sites of Mn(2+) inhibition of ATP production in isolated liver, brain, and heart mitochondria. This approach has several advantages. First, the target tissue for Mn toxicity in the basal ganglia is energetically active and should be studied under rapid phosphorylation conditions. Second, Mn may inhibit metabolic steps which do not affect ATP production rate. This approach allows identification of inhibitions that decrease this rate. Third, mitochondria from different tissues contain different amounts of the components of the metabolic pathways potentially resulting in different patterns of ATP inhibition. Our results indicate that Mn(2+) inhibits ATP production with very different patterns in liver, brain, and heart mitochondria. The primary Mn(2+) inhibition site in liver and heart mitochondria, but not in brain mitochondria, is the F₁F₀ ATP synthase. In mitochondria fueled by either succinate or glutamate+malate, ATP production is much more strongly inhibited in brain than in liver or heart mitochondria; moreover, Mn(2+) inhibits two independent sites in brain mitochondria. The primary site of Mn-induced inhibition of ATP production in brain mitochondria when succinate is substrate is either fumarase or complex II, while the likely site of the primary inhibition when glutamate plus malate are the substrates is either the glutamate/aspartate exchanger or aspartate aminotransferase.

Characteristics and possible functions of mitochondrial Ca(2+) transport mechanisms

Mitochondria produce around 92% of the ATP used in the typical animal cell by oxidative phosphorylation using energy from their electrochemical proton gradient. Intramitochondrial free Ca(2+) concentration ([Ca(2+)](m)) has been found to be an important component of control of the rate of this ATP production. In addition, [Ca(2+)](m) also controls the opening of a large pore in the inner mitochondrial membrane, the permeability transition pore (PTP), which plays a role in mitochondrial control of programmed cell death or apoptosis. Therefore, [Ca(2+)](m) can control whether the cell has sufficient ATP to fulfill its functions and survive or is condemned to death. Ca(2+) is also one of the most important second messengers within the cytosol, signaling changes in cellular response through Ca(2+) pulses or transients. Mitochondria can also sequester Ca(2+) from these transients so as to modify the shape of Ca(2+) signaling transients or control their location within the cell. All of this is controlled by the action of four or five mitochondrial Ca(2+) transport mechanisms and the PTP. The characteristics of these mechanisms of Ca(2+) transport and a discussion of how they might function are described in this paper.

Cyclophilin D interacts with Bcl2 and exerts an anti-apoptotic effect

Cyclophilin D (CypD) is a mitochondrial immunophilin and a key positive regulator of the mitochondrial permeability transition (MPT). Several reports have shown that CypD is overexpressed in various tumors, where it has an anti-apoptotic effect. Because the MPT is a cell death-inducing phenomenon, we hypothesized that the anti-apoptotic effect of CypD is independent of the MPT but is due to its interaction with some key apoptosis regulator, such as Bcl2. Our data indicate that CypD indeed interacts with Bcl2 as confirmed with co-immunoprecipitation, pulldown, and mammalian two-hybrid assays. A cyclophilin D inhibitor, cyclosporine A, disrupts the CypD-Bcl2 interaction. CypD enhances the limiting effect of Bcl2 on the tBid-induced release of cytochrome c from mitochondria, which is not mediated via the MPT. Gain- and loss-of-function experiments confirm that CypD has a limiting effect on cytochrome c release from mitochondria and that such an effect of CypD is cyclosporine A- and Bcl2-dependent. On a cellular level, overexpression or knockdown of CypD respectively decreases or increases cytochrome c release from mitochondria and overall cell sensitivity to apoptosis progressing via the "intrinsic" pathway. Therefore, we here describe a novel function of CypD as a Bcl2 collaborator and an inhibitor of cytochrome c release from mitochondria independent of the MPT. This function of CypD may explain the anti-apoptotic effect of this protein observed in various cancer cells. The fact that some tumors overexpress CypD suggests that this may be an additional mechanism of suppression of apoptosis in cancer.

JEM spotlight: metal speciation related to neurotoxicity in humans

Improved living conditions have led to a steady increase in the life expectancy of humans in most countries. However, this is accompanied by an increased probability of suffering from neurodegenerative diseases like Alzheimer's disease or Parkinson's disease. Unfortunately, the therapeutic possibilities for curing these diseases are very limited up to now. Many studies indicate that a variety of environmental factors contribute to the initiation and promotion of neurodegenerative diseases. For example, the role of metal exposure and disturbance of metal homeostasis in the brain is discussed in this respect. However, most studies focus on the neurological and toxicological aspects but not on a detailed characterisation of the species of the involved metals. Therefore, this review summarizes the neurotoxic effects of selected metals on humans and focuses on contributions from trace element speciation analysis with relevance to neuroscientific research. In spite of the advance in instrumentation and methodology of speciation analysis there are few applications for matrices like cerebrospinal fluid which is due to limited access to these samples and analytical challenges caused by matrix interferences, low concentrations and limited stability of many trace element species of interest. The most relevant neurotoxic metals aluminium, lead, manganese and mercury are reviewed in detail while further metals like cadmium, arsenic, bismuth and tin are briefly discussed. Current results indicate that knowledge on trace element speciation can contribute to a better understanding of the transport of metals across the neural barriers and potentially of their role in diseased human brains.

Manganese accumulates primarily in nuclei of cultured brain cells

Manganese (Mn) is known to pass across the blood-brain barrier and interact with dopaminergic neurons. However, the knowledge on the subcellular distribution of Mn in these cell types upon exposure to Mn remained incomplete. This study was designed to investigate the subcellular distribution of Mn in blood-brain barrier endothelial RBE4 cells, blood-cerebrospinal fluid barrier choroidal epithelial Z310 cells, mesencephalic dopaminergic neuronal N27 cells, and pheochromocytoma dopaminergic PC12 cells. The cells were incubated with 100 microM MnCl(2) with radioactive tracer (54)Mn in the culture media for 24h. The subcellular organelles, i.e., nuclei, mitochondria, microsomes, and cytoplasm, were isolated by centrifugation and verified for their authenticity by determining the markers specific to cellular organelles. Data indicated that maximum Mn accumulation was observed in PC12 cells, which was 2.8, 5.2- and 5.9-fold higher than that in N27, Z310 and RBE4 cells, respectively. Within cells, about 92%, 72%, and 52% of intracellular (54)Mn were found to be present in nuclei of RBE4, Z310, and N27 cells, respectively. The recovery of (54)Mn in nuclei and cytoplasm of PC12 cells were 27% and 69%, respectively. Surprisingly, less than 0.5% and 2.5% of cellular (54)Mn was found in mitochondrial and microsomal fractions, respectively. This study suggests that the nuclei may serve as the primary pool for intracellular Mn; mitochondria and microsomes may play an insignificant role in Mn subcellular distribution.

Role of cyclophilin D in the resistance of brain mitochondria to the permeability transition

The mitochondrial permeability transition (MPT) is involved in both necrosis and apoptosis. Cyclophilin D (CypD) is an important component of the MPT. Brain mitochondria are more resistant to the MPT when compared to heart or liver mitochondria. We found that this increased resistance correlates with low expression of CypD in brain when compared to heart or liver. In newborn rats, sensitivity of brain mitochondria to the MPT and CypD expression are significantly higher than in mature animals. In an in vitro model of neuronal development, mitochondria in differentiated neuronal-like cells exert a higher calcium threshold toward MPT induction and express significantly less CypD when compared to undifferentiated precursor cells. Gain and loss of function experiments confirm the role of CypD in sensitivity to the MPT. Together our data indicate that the increased calcium threshold of brain mitochondria to the MPT correlates with low expression of CypD in brain; and that neuronal cells lose CypD during differentiation and become less sensitive to the MPT induction. This may be a protection mechanism that raises the threshold of brain tissue against injuries.

Manganese-induced apoptosis in rat myocytes

Manganese can be toxic to the heart, causing dysfunction following long exposure. In our experiments, we examined the cytotoxicity of manganese in neonatal rat ventricular myocytes (NRVM) by MTT assays in vitro. Results showed that after incubation in the different concentrations of manganese for 24 h, apparent cytotoxicity was observed. At 500, 1000, and 1500 2 microM of manganese, the percentage of cell viability dropped to 82% +/- 6.13, 78% +/- 5.28, and 66% +/- 4.22, respectively. When cells were treated for 48 h, all concentrations tested exerted toxic effect; especially from 500 to 1500 microM the cell viability dropped from 67% +/- 4.84 to 37% +/- 3.25. Apoptosis in NRVM was then examined by flow cytometry. Results showed that the percentage of apoptotic cells treated with 500 microM of manganese for 24 h increased from 4% +/- 0.84 to 7% +/- 1.16. After 48 h of incubation, this percentage increased to 11% +/- 0.91. There was no significant difference between control groups (0 microM manganese) after 24 and 48 h incubation. The morphological changes of NRVM nuclei were visualized with the fluorescent DNA-binding dye Hoechst33342 after incubation in 500 microM of manganese for 48 h. Compared with normal nuclei, apoptotic nuclei showed the typical features of fragmentation and condensation. To investigate whether there are any apoptotic gene expression changes during apoptosis, we examined the expression level of Bcl-2, Bax, and P53 mRNAs after treatment with 500 microM of manganese for 48 h. The Bcl-2 mRNA expression decreased while the expression of Bax as well as P53 mRNAs increased. These results suggested that manganese cytotoxicity on NRVM could induce apoptosis in NRVM cells. The apoptosis process might involve, and be promoted by, the changes of the expression levels of P53, Bcl-2, and Bax proteins.

Normal cellular prion protein protects against manganese-induced oxidative stress and apoptotic cell death

The normal prion protein is abundantly expressed in the central nervous system, but its biological function remains unclear. The prion protein has octapeptide repeat regions that bind to several divalent metals, suggesting that the prion proteins may alter the toxic effect of environmental neurotoxic metals. In the present study, we systematically examined whether prion protein modifies the neurotoxicity of manganese (Mn) by comparing the effect of Mn on mouse neural cells expressing prion protein (PrP(C)-cells) and prion-knockout (PrP(KO)-cells). Exposure to Mn (10microM-10mM) for 24 h produced a dose-dependent cytotoxic response in both PrP(C)-cells and PrP(KO)-cells. Interestingly, PrP(C)-cells (EC(50) 117.6microM) were more resistant to Mn-induced cytotoxicity, as compared to PrP(KO)-cells (EC(50) 59.9microM), suggesting a protective role for PrP(C) against Mn neurotoxicity. Analysis of intracellular Mn levels showed less Mn accumulation in PrP(C)-cells as compared to PrP(KO)-cells, but no significant changes in the expression of the metal transporter proteins transferrin and DMT-1. Furthermore, Mn-induced mitochondrial depolarization and reactive oxygen species (ROS) generation were significantly attenuated in PrP(C)-cells as compared to PrP(KO)-cells. Measurement of antioxidant status revealed similar basal levels of glutathione (GSH) in PrP(C)-cells and PrP(KO)-cells; however, Mn treatment caused greater depletion of GSH in PrP(KO)-cells. Mn-induced mitochondrial depolarization and ROS production were followed by time- and dose-dependent activation of the apoptotic cell death cascade involving caspase-9 and -3. Notably, DNA fragmentation induced by both Mn treatment and the oxidative stress inducer hydrogen peroxide (100microM) was significantly suppressed in PrP(C)-cells as compared to PrP(KO)-cells. Together, these results demonstrate that prion protein interferes with divalent metal Mn uptake and protects against Mn-induced oxidative stress and apoptotic cell death.

Direct effects of manganese compounds on dopamine and its metabolite Dopac: an in vitro study

Following combustion of fuel containing the additive methylcyclopentadienyl-manganese-tricarbonyl (MMT), manganese phosphate (MnPO(4)) and manganese sulfate (MnSO(4)) are emitted in the atmosphere. Manganese chloride (MnCl(2)), another Mn(2+) species, is widely used experimentally. Using rat striatal slices, we found that MnPO(4) decreased tissue and media dopamine (DA) and media Dopac (a DA metabolite) levels substantially more than either MnCl(2) or MnSO(4); antioxidants were partially protective. Also, both MnCl(2) and MnPO(4) (more potently) oxidized DA and Dopac even in the absence of tissue in the media, suggesting a direct interaction between Mn and DA/Dopac. Because aminochrome is a major oxidation product of DA, we next determined whether MnPO(4) will be more potent in forming aminochrome than MnCl(2) or MnSO(4) which, indeed, was the case. Thus, a potential additional mechanism for the neurotoxic effects of environmentally-relevant forms of Mn, MnPO(4) in particular, is the generation of reactive DA intermediates.

Modulating radiation resistance: Insights based on defenses against reactive oxygen species in the radioresistant bacterium Deinococcus radiodurans

The classical dogma of radiation biology asserts that the cytotoxic effects of ionizing radiation (IR) are principally the result of DNA damage. Yet many organisms that encode a complement of DNA repair functions are killed by IR doses that cause little DNA damage. Instead, proteins likely are the first major class of molecules damaged by IR. This article presents a new perspective on extreme IR resistance in the eubacterium Deinococcus radiodurans, reevaluates the role of superoxide (02*-) ions in IR toxicity, and speculates on potential strategies for controlling resistance in prokaryotes and eukaryotes based on scavenging IR-induced 02*-.

Effects of inhaled manganese on biomarkers of oxidative stress in the rat brain

Manganese (Mn) is a ubiquitous and essential element that can be toxic at high doses. In individuals exposed to high levels of this metal, Mn can accumulate in various brain regions, leading to neurotoxicity. In particular, Mn accumulation in the mid-brain structures, such as the globus pallidus and striatum, can lead to a Parkinson's-like movement disorder known as manganism. While the mechanism of this toxicity is currently unknown, it has been postulated that Mn may be involved in the generation of reactive oxygen species (ROS) through interaction with intracellular molecules, such as superoxide and hydrogen peroxide, produced within mitochondria. Conversely, Mn is a required component of an important antioxidant enzyme, Mn superoxide dismutase (MnSOD), while glutamine synthetase (GS), a Mn-containing astrocyte-specific enzyme, is exquisitely sensitive to oxidative stress. To investigate the possible role of oxidative stress in Mn-induced neurotoxicity, a series of inhalation studies was performed in neonatal and adult male and female rats as well as senescent male rats exposed to various levels of airborne-Mn for periods of time ranging from 14 to 90 days. Oxidative stress was then indirectly assessed by measuring glutathione (GSH), metallothionein (MT), and GS levels in several brain regions. MT and GS mRNA levels and regional brain Mn concentrations were also determined. The collective results of these studies argue against extensive involvement of ROS in Mn neurotoxicity in rats of differing genders and ages. There are, however, instances of changes in individual endpoints consistent with oxidative stress in certain brain tissues.

Speciation of manganese in cells and mitochondria: a search for the proximal cause of manganese neurotoxicity

Recent studies of speciation of manganese (Mn) in brain mitochondria, neuron-like cells, and astrocytes are reviewed. No evidence is found for oxidation of Mn(2+) complexes to a Mn(3+) complex. The only evidence for any Mn(3+) complex is found in a spectrum essentially identical to that of mitochondrial manganese superoxide dismutase (MnSOD). While this does not prove that no Mn(3+) is produced in these tissues by oxidation of Mn(2+), it does suggest that formation of an active Mn(3+) complex by oxidation of Mn(2+) probably does not play as important a role in Mn toxicity as has been suggested earlier. Since these results suggest that we should look elsewhere for the proximal causes of Mn neurotoxicity, we consider the possibilities that Mn(3+) may be transported into the cell via transferrin and that Mn(2+) may inhibit Ca(2+)-activation and control of the rate of ATP production by oxidative phosphorylation.